tty: serial: samsung_tty: Add support for Apple UARTs

Apple SoCs are a distant descendant of Samsung designs and use yet
another variant of their UART style, with different interrupt handling.

In particular, this variant has the following differences with existing
ones:

* It includes a built-in interrupt controller with different registers,
  using only a single platform IRQ

* Internal interrupt sources are treated as edge-triggered, even though
  the IRQ output is level-triggered. This chiefly affects the TX IRQ
  path: the driver can no longer rely on the TX buffer empty IRQ
  immediately firing after TX is enabled, but instead must prime the
  FIFO with data directly.
Signed-off-by: Hector Martin <marcan@marcan.st>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Tested-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210304213902.83903-25-marcan@marcan.stSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/Kconfig

@@ -236,7 +236,7 @@ config SERIAL_CLPS711X_CONSOLE
 
 config SERIAL_SAMSUNG
 	tristate "Samsung SoC serial support"
-	depends on PLAT_SAMSUNG || ARCH_S5PV210 || ARCH_EXYNOS || COMPILE_TEST
+	depends on PLAT_SAMSUNG || ARCH_S5PV210 || ARCH_EXYNOS || ARCH_APPLE || COMPILE_TEST
 	select SERIAL_CORE
 	help
 	  Support for the on-chip UARTs on the Samsung S3C24XX series CPUs,

include/linux/serial_s3c.h

@@ -246,6 +246,22 @@
 				 S5PV210_UFCON_TXTRIG4 |	\
 				 S5PV210_UFCON_RXTRIG4)
 
+#define APPLE_S5L_UCON_RXTO_ENA		9
+#define APPLE_S5L_UCON_RXTHRESH_ENA	12
+#define APPLE_S5L_UCON_TXTHRESH_ENA	13
+#define APPLE_S5L_UCON_RXTO_ENA_MSK	(1 << APPLE_S5L_UCON_RXTO_ENA)
+#define APPLE_S5L_UCON_RXTHRESH_ENA_MSK	(1 << APPLE_S5L_UCON_RXTHRESH_ENA)
+#define APPLE_S5L_UCON_TXTHRESH_ENA_MSK	(1 << APPLE_S5L_UCON_TXTHRESH_ENA)
+
+#define APPLE_S5L_UCON_DEFAULT		(S3C2410_UCON_TXIRQMODE | \
+					 S3C2410_UCON_RXIRQMODE | \
+					 S3C2410_UCON_RXFIFO_TOI)
+
+#define APPLE_S5L_UTRSTAT_RXTHRESH	(1<<4)
+#define APPLE_S5L_UTRSTAT_TXTHRESH	(1<<5)
+#define APPLE_S5L_UTRSTAT_RXTO		(1<<9)
+#define APPLE_S5L_UTRSTAT_ALL_FLAGS	(0x3f0)
+
 #ifndef __ASSEMBLY__
 
 #include <linux/serial_core.h>